Stability,Molecular Separation And Ion Selectivity Of A Two-Dimensional Vermiculite Lamellar Membrane

Membrane separation technology is an efficient,economical and green separation technology,which has been widely used in the fields of medicine,food,environmental protection,biology,metallurgy,chemical industry,petroleum,energy,electronics,bionics,etc.,and has produced huge social and economic benefits,Has become one of the most important technical means in separation science today.The two-dimensional layered membrane has excellent permeability and precise selection and sieving.It has shown the advanced nature of new membrane materials in many fields such as seawater desalination,energy conversion,and organic solvent nanofiltration.It has become membrane separation and nanotechnology.The popular research of,has broad application prospects in the field of modern separation.However,the complex synthesis of the two-dimensional nanosheets constituting the layered film,large pollution,poor structural stability,and poor chemical environment tolerance severely limit their actual production and application.Here,we use natural mineral vermiculite（VMT）to prepare single-layer nanosheets through a simple ion exchange method,and use VMT nanosheets as structures to form a VMT layered membrane layer by layer.We explored the presence of molecules and ions in the vermiculite layer.The main contents of the separation performance and influence mechanism in the film are as follows:（1）A single layer of large-size VMT nanosheets are stacked to form a layered film with a complete and orderly structure and uniform stacking.A single layer of vermiculite nanosheets with a lateral size of approximately～12μm was obtained by the ion exchange method.This process is simple,green,and pollution-free.The single-layer nanosheets are vacuum filtered to obtain the VMT layered membrane.The morphology and structure of VMT nanosheets and VMT layered films were characterized by experimental instruments such as scanning electron microscope,X-ray diffractometer,and atomic force microscope.It is verified that the VMT nanosheets have complete morphology,large lateral size,highly ordered film layer structure,and uniform stacking.（2）The film exhibits good stability in different chemical environments such as strong acid,strong base,strong oxidant,organic solvent,etc.The film surface is still intact after 20 minutes of ultrasound,without cracking,and exhibits excellent mechanical properties.（3）It is superior to the existing commercial membranes in terms of the separation of molecules and organic solvents.It has excellent methanol permeability and good dye molecule retention.By optimizing the membrane structure,the methanol permeability is further increased to 490m^-2h^-1bar^-1,exceeding the limit of existing nanofiltration membranes.（4）The surface charge control effect is the main mechanism of ion transport across the membrane.This unipolar transport mode has far-reaching research significance in applications such as reverse electrodialysis,induction devices,and ion pumps.VMT film provides new opportunities for the application of two-dimensional material films in the fields of environment and energy.